The adenine nucleotide content of mammalian cells is held within a rather narrow concentration range despite marked changes in cell metabolism. This indicates that the rates of synthesis and catabolism are carefully regulated. In ascites tumor cells the rate of catabolism of the adenine nucleotides can be accelerated far beyond the rate of synthesis by addition of 2-deoxyglucose, a non-glycolyzable hexose. Cells treated with 2-deoxyglucose accumulate AMP and the AMP is converted to inosine monophosphate by adenylate deaminase. The 2-deoxyglucose is phosphorylated by hexokinase and ATP and the intracelluar inorganic phosphate (Pi) concentration decreases. Similar increases in the AMP concentration occurs in ascites tumor cells treated with an uncoupler of oxidative phosphorylation. However, in this situation the intracellular Pi concentration increases and there is no change in the total adenine nucleotide concentration. In this work we will study the interrelationships between the intracellular Pi concentrations and the adenine nucleotide degradation in intact ascites tumor cells. The results from these experiments will be applied to a study of the adenylate deaminase reaction in a cell-free system. The effect of Pi and other factors and the rate of AMP conversion to inosine monophosphate will be determined.